A thin film magnetic head used in a magnetic disc apparatus or the like is constituted by parts obtained by machining a bar-like ceramic (hereinafter, referred to as a ceramic bar) on the surface of which a number of element portions made of magnetic thin film or the like for constituting an inductive magnetic converting element or a magnetic resistor element (hereinafter, referred to as an MR element) or the like are formed in a row. A number of the element portions are initially simultaneously formed on a wafer-like ceramic substrate. This ceramic substrate is cut in one direction into a bar-shape to obtain the above-described ceramic bar.
A number of these element portions are simultaneously formed in the wafer-ceramic substrate by using machining technology and thin film technology that are represented by semiconductor manufacturing technology. In this process, for the respective thin films as for measuring a magnetic resistance, a magnetic pole, a coil, insulation or the like, film formation, photoresist coating, exposure for wiring shape or the like, removing no-exposed photoresist, etching of film in no-exposed portion, removing the photoresist in the exposure portion and the like are performed. Thereafter, a protective film is formed on an uppermost layer to finish the forming steps of the element portions.
In the next step, machining such as lapping in which a throat height, an MR height or the like of each element portion is machined to a suitable value is performed for the ceramic bar where a plurality of element portions are formed. In general, in the magnetic disc apparatus, in order to stabilize the output characteristics from the magnetic head, it is necessary to keep the distance between the magnetic polarity portion of the magnetic head and the surface of the recording media at a very short constant distance. The throat height or the MR height is important parameters for restricting this distance.
After the predetermined throat height or the like is obtained in each element portion, machining for forming a surface slanted to the lapped surface lapping an end portion, machining for making curved surface or grooving the lapped surface is further performed. After that step, the ceramic bar is cut into individuals one by one for each element portion. Each element portion constitutes a part of the magnetic head for the magnetic disc apparatus. The ceramic portion of this part is used as a slider lifted by the air blow pressure caused by the rotation of the disc above the magnetic disc when the magnetic head is used in the magnetic disc apparatus. The element portion is used as a head core for performing the recording and/or reproducing of the magnetic signal of the disc.
Note that the throat height means a length (height) of the portion that is a magnetic end portion for performing the recording/reproducting of the magnetic signal in such a head core and where the two magnetic polarities face each other with a fine gap. Also, the MR height means a length (height) from the end portion on the side facing the medium of the MR element to the end portion on the opposite side. In order to make it possible to record/reproduce the signal suitably, it is necessary to select the values of the throat height and the MR height to predetermined values. A high precision is needed for the lapping machining for obtaining these predetermined values.
Also, as described above, the slider is kept in the condition that the slider is lifted at a fine interval away from the disc surface by the air blow pressure of the air flow generated in concomitant with the high speed rotation of the disc. In order to perform the readout of the information from the disc or the write of the information to the disc by the element portion with high precision, it is necessary to always stabilize the lifting height of the lifted slider and the posture of the slider upon lifting. The above-described machining or the like for making the curved surface is effected to the slider so that the slider may be lifted in a stabilized manner.
However, since in general, the above-described ceramic bar has a strain, a curve or the like due to the stress generated by the formation of the element portion or the cut away process performed on the ceramic substrate, it is difficult to obtain the above-described high machining precision simply by fixing the ceramic bar and performing the lapping machining. For this reason, the apparatus for performing the lapping of the magnetic head in the form of the ceramic bar with high precision, that is not a general lapping apparatus, is disclosed in, for example, U.S. Pat. No. 5,620,356. Also, the present applicant of this application proposes several such apparatus and methods (Japanese Patent Application No. 11-162799 or the like).
The method for machining the ceramic bar and obtaining the predetermined throat height or the like will now be described. First of all, the surface, opposite the lapping surface, of the ceramic bar is bonded to a jig with adhesives or the like and the surface to be lapped of the ceramic bar is pushed against the lapping surface of the lapping plate through the jig to perform the lapping the surface to be polished. This jig is subjected to the load from the outside and so forth so that the portion for supporting the ceramic bar is deformed and simultaneously the ceramic bar is also deformed. As result, it is possible to correct the curvature or the like of the ceramic bar itself.
In accordance with this method or using the apparatus in this method, it is possible to perform the above-described machining for making the curved surface (hereinafter, referred as R machining). However, as a matter of fact, since it is difficult to obtain the smooth curved surface (hereinafter, referred as R shape) in view of the structure of the apparatus, in general, the R machining is performed by using an apparatus that is different from these apparatus. Out of the R shapes, a shape in which a central portion of the lapping surface projects to form a part of a spherical surface is particularly called a crown shape. The machining for obtaining the crown shape is called crown machining. The present applicant proposes the apparatus and method disclosed in, for example, Japanese Patent Application Laid-open No. 11-302305 as the lapping apparatus and method for performing the crown machining to each slider.
The lapping method for performing the crown machining to the ceramic bar disclosed by the present applicant will now be described. In order to impart a predetermined crown shape to the ceramic bar, the lapping surface of the lapping plate made of, for example, tin used for lapping the ceramic bar is formed into a conical shape made of a substantially concave surface forming a part of the spherical surface having a predetermined radius. During polishing, the ceramic bar is held by a laterally elongated jig extending in the longitudinal direction of the ceramic bar. More specifically, the surface, opposite the lapping surface of the ceramic bar, is sucked to the elastic material such as a rubber plate or the like attached to one end surface of the laterally elongated jig with adhesives so that the ceramic bar is held at one face of the jig.
The central portion of the jig is subjected to the load so that the ceramic bar is pushed against the lapping surface, and the crown shape is formed to the surface to be lapped of the ceramic bar. At the same time, the suitable load is applied to both end portions thereof. As a result, the non-uniformity in the longitudinal direction of the crown shape formed in the ceramic bar may be reduced. Furthermore, the MR value of the MR element formed in the ceramic bar is measured during polishing. The load for pushing the ceramic bar to the lapping surface is controlled on the basis of the measurement result to thereby control the lapping amount upon crown machining.